This invention relates to refrigerators having a sandwiched cabinet construction of a metal outer casing and a plastic inner liner separated by foamed-in-place insulation bonding the two together.
Refrigerator cabinet constructions having a sandwiched wall structure of a metal outer casing and an inner plastic food liner maintained in a sufficiently structurally rigid relationship by foamed-in-place polyurethane foam insulation along with the attendant advantages and disadvantages of such construction is well known in the refrigerator cabinet making technology. One of the known advantages of a plastic inner liner is its ability to be molded into a configuration providing various support structures including a mullion partition separating the freezer compartment from the fresh food compartment in a refrigerator. However, it is well known that plastic is generally weak in tension and also exhibits a coefficient of expansion many times that of the metal outer casing. Taking these characteristics into consideration, it is realized that securely bonding the plastic inner liner to the metal outer casing through the adhesive qualities of the foamed-in-place insulation would result in the inner liner being subjected to tension forces due to a difference in expansion and contraction of the liner relative to the outer metal casing. The liner would also be subjected to tension forces whenever the inner liner was exposed to temperatures less than the outer wrapper. As this last condition, in fact, describes the general operating condition of a refrigerator, it was found to be necessary to alleviate the transmission of such forces to the inner liner by separating the inner liner from the foamed insulation by a parting agent which would then accommodate the variations in rates of expansion or contraction without developing the tensioning stress. However, use of such a parting agent severely reduces the structural integrity of the complete cabinet structure, or by selectively applying a release agent in those areas of the inner liner facing the foamed insulation that corresponded to structure giving rise to stress concentrations. This latter arrangement, although obviously relieving the inner liner in those high stress areas, in endeavoring to retain the structural integrity of the cabinet would still, under extreme conditions, transmit sufficient tensioning stress to the inner liner to cause it to fracture, especially if the refrigerator is subjected to extremely low temperatures. Such extremely low temperatures may be experienced when the refrigerators are transported through geographical regions where the temperatures may reach -20 F. and lower.